CN113884019A

CN113884019A - Three-dimensional imaging system and method

Info

Publication number: CN113884019A
Application number: CN202010630512.1A
Authority: CN
Inventors: 杜德涛; 陈如新
Original assignee: Ruifu Technology Beijing Co ltd
Current assignee: Ruifu Technology Beijing Co ltd
Priority date: 2020-07-03
Filing date: 2020-07-03
Publication date: 2022-01-04
Anticipated expiration: 2040-07-03
Also published as: CN113884019B; WO2022001493A1; US20230143702A1

Abstract

The application discloses three-dimensional imaging system includes: an optical transmitter that transmits light pulses to a target scene; an optical modulator that modulates an optical state of at least a portion of the light pulses emitted from the optical emitter and/or returned from the target scene; an array of optical elements receiving the modulated return portion, wherein the array of optical elements has the function of transmitting light in at least three mutually different optical states at least within a first preset time range before emission of the light pulse and/or within a second preset time range after emission of the light pulse; a photodetector including an imaging lens that receives the optical signal passing through the optical element array and converts the received optical signal into an electrical signal; and a controller applying control to the optical modulator through the electrical circuit, the optical modulator modulating the optical state of the light pulse as a function of time based on the control, and the controller calculating the distance and/or relative light intensity based on the electrical signal and the applied control.

Description

Three-dimensional imaging system and method

Technical Field

The present application relates to the field of optical imaging, and more particularly to three-dimensional imaging systems and related methods for capturing three-dimensional information.

Background

In some conventional three-dimensional imaging systems, three-dimensional coordinates of a target object are obtained by illuminating the object with laser pulses and using a kerr box or pockels box to change the polarization state of the laser pulses reflected from the object as a function of time. As a result, the polarization state of portions of the laser pulse reflected by features of the target object closer to the imaging system (having shorter times of flight) are affected to a lesser extent, while the polarization state of portions of the laser pulse reflected by features of the target object further from the imaging system (having longer times of flight) are affected to a greater extent. By imaging the two polarization components of the polarization modulated laser beam on two separate focal plane arrays, positional information about the target object can be calculated.

However, the above method requires calibration and alignment of images acquired at two focal planes, and is prone to error. In addition, the above method adds many additional optical devices in order to separate polarization states, thereby resulting in more complicated optical design and increased cost and system size and weight.

In some existing solutions, the time of flight can be determined based on the polarization state of the optical signal, typically by: the intensity of the optical signal passing through the two linear polarizers is detected along with the modulation of the polarization direction of the optical signal by the electro-optical modulator, wherein the polarization directions of the linear polarizer arranged in front of the electro-optical modulator and the linear polarizer arranged behind the electro-optical modulator are not parallel. However, due to the linear polarizers arranged before and after the electro-optical modulator, the energy of the optical signal from the target scene is greatly reduced and the amount of transmitted light is low, thereby causing low measurement accuracy or demanding requirements on the imaging chip.

Disclosure of Invention

The three-dimensional imaging system and the method for measuring by using the three-dimensional imaging system can solve or partially solve the problems in the prior art.

The three-dimensional imaging system according to the first aspect of the present application may comprise: an optical transmitter that transmits light pulses towards a target scene that returns at least a portion of the light pulses. The three-dimensional imaging system may further include: an optical modulator that modulates an optical state of at least a portion of the light pulses emitted from the optical emitter and/or returned from the target scene; an array of optical elements receiving at least a portion of the modulated light pulses, wherein the array of optical elements has the function of transmitting light in at least three mutually different optical states, which may include but are not limited to polarization state, transmittance, reflectance, at least within a first preset time range before emission of the light pulses and/or within a second preset time range after emission of the light pulses; a photodetector including an imaging lens that receives the optical signal passing through the optical element array and converts the received optical signal into an electrical signal; and a controller applying control to the optical modulator by a circuit, the optical modulator modulating the optical state of the light pulses emitted from the optical emitter and/or at least a portion of the light pulses returned from the target scene as a function of time based on the control, and the controller calculating the distance between each pixel point in the target scene and the optical emitter and/or the relative light intensity of each pixel point in the target scene based on the electrical signal from the photodetector and the control applied to the optical modulator.

In one embodiment, the optical state may be a polarization state of light.

In one embodiment, the array of optical elements may include at least three polarizers having fixed polarization directions different from each other.

In one embodiment, the array of optical elements comprises at least one polarization component with adjustable polarization direction.

In one embodiment, the array of optical elements is comprised of four polarizers, the four polarizing components being arranged in a grid-like fashion.

In one embodiment, the optical element array includes at least one optical element array unit, each of the at least one optical element array unit including at least three polarization members having polarization directions different from each other; and the photodetector includes at least one photodetector cell corresponding to the at least one optical element array cell.

In one embodiment, the optical element array unit includes four polarizing plates arranged in a matrix shape.

In one embodiment, the four polarizing members are a 0 ° directional polarizing plate, a 45 ° directional polarizing plate, a 90 ° directional polarizing plate, and a 135 ° directional polarizing plate, respectively.

In one embodiment, three of the at least three polarization members having polarization directions different from each other are a 0 ° directional linear polarizer, a 45 ° directional linear polarizer, and a left-or right-handed polarizer, respectively.

In one embodiment, the array of optical elements comprises a thin film polarizer, a wire grid polarizer, a prismatic polarizer, a liquid crystal polarizer, or a combination thereof.

In one embodiment, the optical modulator comprises a crystal with electro-optic modulation effect, a liquid crystal, and/or a crystal with acousto-optic modulation effect, a liquid crystal.

In one embodiment, the optical modulator comprises a plurality of optical modulators, the plurality of optical modulators being connected in series.

In one embodiment, the controller is in unidirectional communication with the optical emitter and the optical modulator, and the controller is in bidirectional communication with the photodetector.

In one embodiment, the array of optical elements and the photodetector are integrally integrated.

In one embodiment, the optical emitter and the photodetector are integrated integrally or separately.

In one embodiment, the light pulse has a wavelength of 300nm to 750nm, 700nm to 1000nm, 900nm to 1600nm, 1um to 5um, or 3um to 15 um.

In one embodiment, the light pulses have a pulse width of 0.1ps to 5ns, 1ns to 100ns, 100ns to 10us, or 10us to 10 ms.

In one embodiment, the photodetector comprises a silicon-based detector CCD, CMOS, and/or Ge, InGaAs, InSb, InAs, HgCaTe, QWIP detector or detector array.

In one embodiment, the three-dimensional imaging system further comprises an imaging lens disposed between the optical modulator and the array of optical elements.

In one embodiment, the three-dimensional imaging system further comprises a linear polarizer and/or a circular polarizer disposed on a side of the optical modulator proximate to the target scene.

In another aspect, the present application also provides a method of forming a three-dimensional imaging system, comprising: arranging an optical modulator on an optical path of an optical emitter so that pulsed light emitted by the optical emitter has a time-varying optical state as it returns through a target scene; receiving the optical signal modulated by the optical modulator through an optical element array, wherein the optical element array comprises at least three polarization components having polarization directions different from each other; disposing a photodetector behind the array of optical elements to receive optical signals passing through the array of optical elements and to convert the received optical signals into electrical signals; and providing a controller in electrical communication with the optical emitter, the optical modulator, and the photodetector, wherein the controller applies control to the optical modulator that modulates a return portion of the light pulse as a function of time based on the control, and the controller calculates a distance between each pixel in the target scene and the optical emitter and/or a relative light intensity of each pixel in the target scene based on the electrical signal from the photodetector and the control applied to the optical modulator.

In one embodiment, the controller applies control to the optical modulator via a circuit, the optical modulator modulating the optical state of the return portion of the light pulse as a monotonic function of time based on the control.

In one embodiment, the method of forming a three-dimensional imaging system further comprises disposing a lens between the object scene and the array of optical elements.

In another aspect, the present application also provides a method for ranging using the three-dimensional imaging system as described above, the method including: shooting the target scene for the first time at an initial time point to obtain reference image information; and shooting for the second time at the next time point separated from the initial time point by preset time to obtain comparison image information, wherein the distance between each pixel point in the target scene and the optical emitter and/or the relative light intensity of each pixel point in the target scene are determined based on the reference image information and the comparison image information.

In yet another aspect, the present application further provides a method for ranging using the three-dimensional imaging system as described above, the method including: calibrating the three-dimensional imaging system; and shooting once at a preset time point to obtain image information, and determining the distance between each pixel point in the target scene and the optical emitter and/or the relative light intensity of each pixel point in the target scene based on the image information and system calibration information.

In another aspect, the present application also provides a method for ranging using the three-dimensional imaging system as described above, the method comprising: modulating, by the optical modulator, an optical signal returned by the pulsed light emitted by the optical emitter via the target scene; receiving the optical signal modulated by the optical modulator through an optical element array, wherein the optical element array comprises at least three polarization components having polarization directions different from each other; receiving an optical signal passing through the optical element array using a photodetector, and converting the received optical signal into an electrical signal; and applying, by a controller, control to the optical modulator, the optical modulator modulating a return portion of the light pulse as a function of time based on the control; and calculating, by the controller, a distance between each pixel in the target scene and the optical emitter and/or a relative light intensity of each pixel in the target scene based on the electrical signal from the photodetector and the control applied to the optical modulator.

In yet another aspect, the present application also provides a method for ranging using the three-dimensional imaging system as described above, the method comprising: modulating, by the optical modulator, an optical signal returned by the pulsed light emitted by the optical emitter via the target scene; receiving the optical signal modulated by the optical modulator through an optical element array, wherein the optical element array comprises at least one optical component which transmits light of at least three optical states different from each other at least for a predetermined time; receiving an optical signal passing through the optical element array using a photodetector, and converting the received optical signal into an electrical signal; applying, by a controller, a control to the optical modulator, the optical modulator modulating a return portion of the light pulse as a function of time based on the control; and calculating, by the controller, a distance between each pixel in the target scene and the optical emitter and/or a relative light intensity of each pixel in the target scene based on the electrical signal from the photodetector and the control applied to the optical modulator.

Drawings

The exemplary embodiments will be more clearly understood from the following brief description in conjunction with the accompanying drawings. The drawings illustrate non-limiting exemplary embodiments described herein. In the drawings:

FIG. 1 shows a schematic diagram of a three-dimensional imaging system according to an exemplary embodiment of the present disclosure;

FIG. 2 shows a schematic diagram of a three-dimensional imaging system according to another exemplary embodiment of the present disclosure;

fig. 3A illustrates a schematic diagram of a polarizer array unit according to an exemplary embodiment of the present disclosure;

fig. 3B illustrates a schematic view of a polarizer array unit according to another exemplary embodiment of the present disclosure;

fig. 3C shows a schematic diagram of a dynamic polarizer according to yet another exemplary embodiment of the present disclosure;

FIG. 4 illustrates a Poincare sphere model;

FIG. 5 shows a schematic diagram of determining time of flight using a Poincare sphere model;

FIG. 6 shows a schematic diagram of a three-dimensional imaging system according to an exemplary embodiment of the present disclosure;

FIG. 7 shows a block diagram of a method for forming a three-dimensional imaging system according to an example embodiment of the present application; and

fig. 8 illustrates a block diagram of a method for ranging using a three-dimensional imaging system according to an exemplary embodiment of the present application.

Detailed Description

For a better understanding of the present application, various aspects of the present application will be described in more detail with reference to the accompanying drawings. It should be understood that the detailed description is merely illustrative of exemplary embodiments of the present application and does not limit the scope of the present application in any way. Like reference numerals refer to like elements throughout the specification. The expression "and/or" includes any one of the items listed in relation and any combination of any two or more.

The features described in this application may be embodied in different forms and should not be construed as limited to the examples described in this application. Rather, the examples described in this application are provided merely to illustrate some of the many possible ways to implement the methods, apparatuses, and/or systems described in this application, which will be apparent after understanding the disclosure of this application.

Use of the word "may" with respect to an example or embodiment (e.g., with respect to what an example or embodiment may include or implement) means that there is at least one example or embodiment that includes or implements such a feature, and all examples or embodiments are not limited thereto.

It should be noted that the expressions first, second, etc. in this specification are used only to distinguish one feature from another feature, and do not indicate any limitation on the features. Thus, the first electro-optic modulator discussed below may be referred to as the second electro-optic modulator, which may also be referred to as the first electro-optic modulator, without departing from the teachings of the present application.

In the drawings, the thickness, size, and shape of each component may have been slightly exaggerated for convenience of explanation. In particular, the shapes of the spherical or aspherical surfaces shown in the drawings are shown by way of example. That is, the shape of the spherical surface or the aspherical surface is not limited to the shape of the spherical surface or the aspherical surface shown in the drawings. The figures are purely diagrammatic and not drawn to scale.

Throughout the specification, when an element is described as being "on," "connected to" or "coupled to" another element, for example, it can be directly on, "connected to" or "coupled to" the other element, or one or more other elements may be present between the element and the other element. In contrast, when an element is referred to as being "directly on," "directly connected to" or "directly coupled to" another element, there may be no other elements intervening between the element and the other element.

Spatially relative terms, such as "above … …," "upper," "below … …," and "lower," may be used herein for ease of description to describe one element's relationship to another element as illustrated in the figures. Such spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as "above" or "upper" relative to other elements would then be "below" or "lower" relative to the other elements. Thus, the phrase "above … …" includes both orientations "above … …" and "below … …" depending on the spatial orientation of the device. The device may also be otherwise oriented (e.g., rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.

It will be further understood that the terms "comprises," "comprising," "has," "having," "includes" and/or "including," when used in this specification, specify the presence of stated features, elements, and/or components, but do not preclude the presence or addition of one or more other features, elements, components, and/or groups thereof. Moreover, when a statement such as "at least one of" appears in the list of listed features, that statement modifies all features in the list rather than merely individual elements in the list.

As used herein, the terms "approximately," "about," and the like are used as words of table approximation and not as words of table degree, and are intended to account for inherent deviations in measured or calculated values that can be appreciated by one of ordinary skill in the art.

Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

In addition, the embodiments and features of the embodiments in the present application may be combined with each other without conflict. In addition, unless explicitly defined or contradicted by context, the specific steps included in the methods described herein are not necessarily limited to the order described, but can be performed in any order or in parallel.

Fig. 1 illustrates a schematic diagram of a three-dimensional imaging system 100a according to an exemplary embodiment of the present disclosure, fig. 2 illustrates a schematic diagram of a three-dimensional imaging system 100B according to another exemplary embodiment of the present disclosure, fig. 3A illustrates a schematic diagram of a polarizer array unit according to an exemplary embodiment of the present disclosure, fig. 3B illustrates a schematic diagram of a polarizer array unit according to another exemplary embodiment of the present disclosure, and fig. 3C illustrates a schematic diagram of a dynamic polarizer according to yet another exemplary embodiment of the present disclosure.

Referring to fig. 1, a three-dimensional imaging system 100a may include an optical emitter 10, an optical modulator 20, an array of optical elements 30, a photodetector 40, and a controller 50.

The optical transmitter 10 is used to transmit light pulses towards the target scene to illuminate the target scene. For example, light pulses may be emitted to the target scene according to a preset law. Optical emitter 10 may emit light pulses having wavelengths in the range of, for example, 300nm-750nm, 700nm-1000nm, 900nm-1600nm, 1um-5um, or 3um-15 um. The pulse width may be, for example, 0.1ps-5ns, 1ns-100ns, 100ns-10us, or 10us-10 ms. The parameters of wavelength and pulse width of the light pulses emitted by the optical emitter 10 are exemplified herein by way of example only, however the application is not so limited and other parameters of wavelength and pulse width are permissible without departing from the teachings of the application.

In some embodiments, the optical transmitter 10 may be a semiconductor laser, a fiber laser, a solid state laser. The optical transmitter 10 may also be a mode-locked laser, an actively Q-switched laser, a passively Q-switched laser, or other directly modulated laser.

In some embodiments, the light pulses emitted by the optical emitter 10 may be modulated linearly polarized light, circularly polarized light, elliptically polarized light, or unpolarized light. The pulse repetition frequency of the light pulses may be selected from the range of 1Hz-100Hz, 100Hz-10kHz, 10kHz-1MHz, or 1MHz-100 MHz. The coherence length of the light pulses may be less than 100m, 10m, 1m or 1 mm.

The light pulses emitted by the optical emitter 10 are directed towards the target scene. The target scene may include, for example, the subject 200. The subject 200 reflects or refracts the optical signal from the optical transmitter 10 and guides a part of the signal to the optical modulator 20. At this point, optical modulator 20 may be used to modulate the optical state of at least a portion of the light pulses returning from the target scene.

The arrangement of the optical modulator 20 is not limited thereto, however, and in some embodiments the optical modulator 20 may be arranged between the optical emitter 10 and the target scene for modulating the optical state of the light pulses emitted from the optical emitter.

The optical modulator 20 may include a crystal having an electro-optic modulation effect, and/or a crystal having an acousto-optic modulation effect. The optical modulator 20 may be a variable fabry-perot etalon, and/or a Pockels (Pockels) effect device, a Kerr (Kerr) effect device, or the like.

The crystal having the electro-optical modulation effect (herein, also referred to as "electro-optical crystal") may be, for example, at least one of LiNbO3, BaTiO3, KD × P, ADP, KTN, PLZT, BBO, or the like. The refractive index of the electro-optic crystal may vary in relation to the strength of the electric field applied to the electro-optic crystal, thereby causing a phase delay to be imparted to the optical signal passing through the electro-optic crystal and a corresponding change in the state of refraction of the optical signal. According to an exemplary embodiment, the direction of the electric field applied to the electro-optic crystal may be perpendicular to the propagation direction of the optical signal.

However, the present application is not so limited and any suitable electro-optic crystal material is contemplated as falling within the teachings of the present application, provided that when a certain voltage is applied across the electro-optic crystal, a change in the refractive index of the electro-optic crystal occurs in relation to the strength of the electric field, resulting in a change in the characteristics of the light wave passing through the crystal, enabling modulation of the phase, amplitude, intensity and/or polarization state of the optical signal. The optical modulator 20 may effect modulation of the intensity of the light pulse portions as a function of time.

For electro-optical modulators (EOM), the input polarization P_inAnd an output polarization P_outThe following relationship is satisfied:

where A, B, C, D is a parameter of the jones matrix of the electro-optic modulator that is related to the phase delay of the EOM of each pixel, and e (t) is a modulation signal that varies monotonically with time to provide a one-to-one correlation between time and phase delay.

In general, two measurements need to be made, i.e. no modulation or the modulation signal e (t) is constant, and modulated so that the modulation signal e (t) is a function f (t) over time.

When a fixed polarization component is added in front of the optical modulator 20, the system can be calibrated in advance and then a measurement can be made in actual use using the modulation signal e (t). The flight time and the distance of each pixel corresponding to the space point can be obtained through the one-to-one correspondence relationship between the time and the phase delay.

In some embodiments, the optical modulator 20 may include two electro-optic modulators. For example, as shown in FIG. 2, the optical modulator 20 may include a first electro-optic modulator 21 and a second electro-optic modulator 22. The first electro-optical modulator 21 and the second electro-optical modulator 22 may be connected in series. The optical axis direction of the electro-optical crystal included in the first electro-optical modulator 21 and the optical axis direction of the electro-optical crystal included in the second electro-optical modulator 22 may be perpendicular to each other. However, the present application is not so limited and the optical modulator 20 may also include, for example, three, four, or more electro-optical modulators. The plurality of electro-optical modulators may be connected in series and have different or the same optical axis directions from each other.

By using multiple electro-optic modulators, the voltage required by optical modulator 20 may be significantly reduced. In the case where the optical modulator 20 includes a plurality of electro-optical modulators, the direction of the electric field applied to each electro-optical modulator may be perpendicular to the propagation direction of the optical signal, and the directions of the electric fields applied to the respective electro-optical modulators may be different from each other. For example, the direction of the electric field applied to the first electro-optic modulator 21 may be perpendicular to the direction of the electric field applied to the second electro-optic modulator 22. It will be appreciated that the direction of the electric field applied to each electro-optic modulator may also be parallel to the direction of propagation of the light, or in any other suitable direction that is capable of carrying out the inventive concept.

The array of optical elements 30 has the function of transmitting light in at least three mutually different optical states, including but not limited to polarization state, transmittance, reflectance, at least during a first preset time range before emission of the light pulses and/or during a second preset time range after emission of the light pulses.

The array of optical elements 30 may be formed by an array of polarizers, different areas of which may be used to transmit optical signals having different polarization states. The optical element array 30 may include one or more polarizer array units. The array of optical elements 30, the photodetector 40, and the controller 50 may be used to detect the polarization state of the optical signal. This will be explained in detail below.

The array of optical elements 30 may include thin film polarizers, wire grid polarizers, prism polarizers, liquid crystal polarizers, or combinations thereof. Alternatively, the optical element array 30 may include at least three polarizing plates having fixed polarization directions, the polarization directions of the at least three polarizing plates being different from each other.

In some embodiments, the optical element array 30 may include at least one optical element array unit, each of which includes at least three polarization members having polarization directions different from each other. For example, each optical element array unit may include four linear polarizers. The four linear polarizers are arranged in a matrix shape, and have different polarization directions from each other.

As shown in fig. 3A, each polarizer array unit may include a 0 ° polarizer P ₀45 DEG polarizing plate P ₄₅90 DEG polarizing plate P₉₀And 135 DEG polarizing plate P₁₃₅. One or more polarizer array elements form the optical element array 30. 0 degree polarizing plate P₀Allowing 0 ° polarized light to pass therethrough, 45 ° polarizing plate P₄₅Allowing 45 ° polarized light to pass therethrough, a 90 ° polarizing plate P₉₀Allowing 90 ° polarized light to pass therethrough, and a 135 ° polarizing plate P₁₃₅Allowing 135 ° polarized light to pass therethrough.

In some embodiments, the optical element array 30 may include only one polarizer array unit, i.e., the optical element array 30 may include only one 0 ° polarizer P₀A 45 DEG polarizing plate P₄₅A 90 DEG polarizing plate P₉₀And a 135 DEG polarizing plate P₁₃₅The four polarizing plates are arranged in a matrix shape and each of the polarizing plates has a polarizationThe patch covers a quarter of the area of the rear photodetector 40.

The arrangement of the polarizer array unit is not limited to the arrangement shown in fig. 3A. In some other embodiments, each polarizer array unit may include, for example, three polarizers. The three polarizing plates are arranged in a matrix with a region where no polarizing plate is provided, and have polarization directions different from each other. For example, as shown in fig. 3B, each polarizer array unit may include a region NP where no polarizer is disposed, a 0 ° polarizer P ₀45 DEG polarizing plate P₄₅And a right-handed polarizing plate P_R. The region NP without the polarizer can allow light signals of any polarization state to pass therethrough, the 0 DEG polarizer P₀Allowing 0 ° polarized light to pass therethrough, 45 ° polarizing plate P₄₅Allowing 45 ° polarized light to pass therethrough and a right-handed polarizing plate P_RAllowing optical signals of right-handed polarization to pass therethrough. In some embodiments, each polarizer array unit may be further configured to include a region NP where no polarizer is disposed, a 0 ° polarizer P ₀45 DEG polarizing plate P₄₅And a left-handed polarizing plate P_L(not shown).

It should be understood that the arrangement of the polarizers on the optical element array 30 in the present application is not limited to the combinations described herein, and other polarizer combinations that enable the detection of the polarization state of the optical signal are possible.

Optionally, the array of optical elements 30 may also be formed by at least one polarization element with an adjustable polarization direction. Each polarizer array element may comprise a polarization element with an adjustable polarization direction, e.g. a dynamic polarizer DP with a polarization direction that may vary over time. The polarization direction of the polarization element with adjustable polarization direction can be controllably changed (e.g. by rotating the polarization element at high speed or by voltage modulation), for example such that the polarization direction of the polarization element is switched between 0 °, 45 °, 90 ° and 135 °. The polarization directions of the polarization elements with adjustable polarization directions may be sequentially switched in the order of, for example, 0 °, 45 °, 90 °, and 135 °, but the present application is not limited thereto, and the polarization directions of the polarization elements with adjustable polarization directions may be sequentially switched in other angles.

As shown in fig. 3C, the polarization direction of the dynamic polarizer DP may change with time and may, for example, be at the point of time t₁Has a polarization direction of 0 DEG and has a duration Deltat₁At a time point t₂Has a polarization direction of 45 DEG and has a duration Deltat₂At a time point t₃Has a polarization direction of 90 DEG and has a duration Deltat₃And at a point in time t₄Has a polarization direction of 135 DEG and has a duration Deltat₄。△t₁、△t₂、△t₃And Δ t₄May be the same as or different from each other. The switching of the dynamic polarizer DP between different polarization directions may be continuous or intermittent.

In an exemplary embodiment, the polarization direction of the polarization element with adjustable polarization direction can be switched at a very fast speed to realize that the portions with different polarization directions in the optical signal are transmitted at different time points. A

At least one photoelectric detector unit can be arranged behind each polaroid, namely, at least one pixel point corresponding to each polaroid is arranged behind each polaroid. A photodetector cell disposed behind the polarizer may be used to capture the light signal transmitted through the polarizer. In some exemplary embodiments, the array of optical elements 30, including the array of polarizers, may be integrated with the photodetector 40.

Photodetector 40 may include one or more photodetector cells. For example, the photodetector 40 may include one or more CMOS sensors or sensor arrays. Photodetector 40 may convert the received optical signal into an electrical signal. The photodetector 40 may be coupled with the controller 50 to receive control signals from the controller 50 and to transmit detected light intensity signals, for example, to the controller 50. As examples of applications, the photodetector 40 may comprise a silicon-based detector CCD, CMOS, and/or Ge, InGaAs, InSb, InAs, HgCaTe, QWIP detector, or detector array.

Controller 50 may be used to control optical emitter 10, optical modulator 20, and photodetector 40. The controller 50 may be in one/two-way communication with the optical emitter 10, the optical modulator 20, and the photodetector 40 to implement a method for ranging by the three-dimensional imaging system. For example, controller 50 may be in bi-directional communication with optical emitter 10 and photodetector 40, and may be in uni-directional communication with optical modulator 20.

Fig. 8 illustrates a method 800 for ranging with a three-dimensional imaging system according to an exemplary embodiment of the present application. The cooperation of the components of the three-dimensional imaging system 100a of the above-described embodiment of the present application will be further described below with reference to the method of fig. 8.

In step S810, a light signal returned by the pulsed light emitted by the optical emitter 10 via the target scene is modulated by the optical modulator 20.

In step S830, the optical signal modulated by the optical modulator 20 is received by the optical element array 30. The optical element array 30 may include at least three polarization members having polarization directions different from each other. Optionally, the optical element array 30 comprises at least one optical component having a transmission of light of at least three optical states different from each other at least for a predetermined time.

In step S850, the photodetector 40 is used to receive the optical signal passing through the optical element array 30 and convert the received optical signal into an electrical signal.

In step S870, control is applied to the optical modulator 20 by the controller 50, the optical modulator 20 modulates the returned portion of the light pulse as a function of time based on the control, and the distance between each pixel point in the target scene and the optical emitter 10 and/or the relative light intensity of each pixel point in the target scene and other information are calculated by the controller 50 based on the electrical signal from the photodetector 40 and the control applied to the optical modulator 20. Further, the optical transmitter 10 may transmit pulsed light having a preset wavelength and a pulse width based on the pulsed light control signal received from the controller 50. Optical modulator 20 may modulate the phase, amplitude, intensity, and/or polarization state of the optical signal based on receiving the voltage sweep signal from controller 50. The photodetector 40 may capture image information based on a control signal received from the controller 50, while the controller 50 may receive an electrical signal from the photodetector 40.

Controller 50 may calculate the distance of each pixel point in the target scene from the optical emitter, the relative light intensity of each pixel point in the target scene, and/or other information based on the control applied to optical modulator 20 and the receipt of the electrical signal from photodetector 40.

The control exerted by the controller 50 on the optical modulator 20 is not limited to the scheme of applying voltage control, and other possible control schemes such as, but not limited to, current control, control of mechanical components actuated by the circuit, and light control may also be employed without departing from the teachings of the present application.

In an exemplary embodiment, an imaging lens group may be disposed between the optical modulator 20 and the optical element array 30. Alternatively, the imaging lens group may also be disposed between the target scene and the optical modulator 20, or at other suitable locations.

Fig. 4 shows a poincare sphere model. The principle of determining the polarization state of an optical signal will be explained with reference to fig. 4.

The polarization state of the optical signal can be detected by the stokes parameter in combination with the poincare sphere model. Assuming hundred percent polarization (i.e., fully polarized state), the Stokes parameter S₀、S₁、S₂And S₃The calculation can be performed using the method described below.

When the polarizer array shown in fig. 3A is used:

S₀＝L₀+L₉₀

S₁＝L₀-L₉₀

S₂＝L₄₅–L₁₃₅

S₀ ²＝S₁ ²+S₂ ²+S₃ ²

wherein L is₀Is passed through a 0 DEG polarizing plate P₀Light intensity of L₄₅Is passed through a 45 DEG polarizer P₄₅Light intensity of L₉₀Is passed through a 90 DEG polarizer P₉₀Light intensity and L₁₃₅Is passed through a 135 deg. polarizer P₁₃₅The light intensity of (c). The Stokes parameter S can be obtained by the above equation₀、S₁、S₂And S₃The corresponding numerical value of (c).

When the polarizer array shown in fig. 3B is used:

S₀＝L

S₁＝L₀–2L

S₂＝L₄₅–2L

S₃＝L_R–2L

where L is the intensity of light passing through the region NP where no polarizing plate is provided, L is₀Is passed through a 0 DEG polarizing plate P₀Light intensity of L₄₅Is passed through a 45 DEG polarizer P₄₅Light intensity and L_RIs passed through a right-handed polarizing plate P_RThe light intensity of (c). The Stokes parameter S can be obtained by the above equation₀、S₁、S₂And S₃The corresponding numerical value of (c).

Obtaining the Stokes parameter S₁、S₂、S₃After the corresponding numerical value is obtained, the polarization state of the optical signal can be judged by combining the Poincare sphere model. As shown in fig. 4, the two poles of the sphere are characterized by left and right circularly polarized light; each point on the equator represents linearly polarized light with different vibration directions; the upper hemisphere represents left-handed elliptical polarized light; the lower hemisphere features right-handed elliptically polarized light, and so on. Based on S₁、S₂、S₃The corresponding value is clicked on the Poincare sphere model, and the specific polarization state of the optical signal can be obtained.

The process of determining the polarization state of the optical signal in conjunction with the poincare sphere model may be performed in the controller 50. Further, the controller 50 determines a correspondence relationship between the measured polarization state of the optical signal and the control voltage of the optical modulator 20, and determines the time of flight.

Fig. 5 shows a schematic diagram of determining time of flight using a poincare sphere model. The determination method of the time of flight will be described below with reference to fig. 5.

For simplicity, assume lightThe signal is in the fully polarised state and has been normalised, i.e. S₁ ²+S₂ ²+S₃ ²The polarization state positions of the optical signals are all on the sphere of the poincare sphere 1. When the first photographing is performed at the initial time point, the initial polarization state W of the optical signal can be obtained. As the voltage applied to the optical modulator 20 increases from small to large, the polarization state of the optical signal is changed, and the corresponding position on the poincare sphere is changed accordingly. The optical signal that reaches the optical modulator 20 first in time has a small change in polarization state, and therefore the polarization state is closer to the point W on the poincare sphere; the optical signal that reaches the optical modulator 20 after the time is changed greatly in polarization state, and thus the polarization state is farther from the point W on the poincare sphere. When the second shot is performed at the next time point, the optical signal whose initial position (polarization state) is W moves along the spherical surface to the end position V. Different points on the curve WV correspond to different times of flight. The location of the two points W, V is determined and the distance corresponding to point V is determined based on the control voltage of the optical modulator 20.

According to the above principle, the method for ranging using the three-dimensional imaging system 100a as illustrated in fig. 1 may include: shooting the target scene for the first time at an initial time point to obtain reference image information; and shooting for the second time at the next time point separated from the initial time point by preset time to obtain comparison image information, wherein the distance between each pixel point in the target scene and the optical emitter and/or the relative light intensity of each pixel point in the target scene are determined based on the reference image information and the comparison image information.

It should be noted that, assuming that the optical signal is in a full polarization state, only for the purpose of simplifying the model, the method for determining the polarization state, the time of flight and calculating the distance according to the present application can be applied to the optical signal having any polarization state. When the optical signal is not in a fully polarized state, the starting point and the ending point may both be located within the sphere.

The determination of the polarization state of the optical signal using the above method has less limitation on the optical signal in the initial state, that is, the optical signal in the initial state may be an optical signal having any polarization state, which can effectively reduce the loss of optical energy. In addition, with the ranging method as described above, measurement can be performed using a CMOS sensor plus a polarizer array directly without additional provision of another sensor array.

Fig. 6 shows a schematic diagram of a three-dimensional imaging system 100c according to an exemplary embodiment of the present disclosure.

The three-dimensional imaging system 100c shown in fig. 6 differs from the three-dimensional imaging system 100a shown in fig. 1 in that the three-dimensional imaging system 100c in fig. 6 may further include a polarizer 60 disposed in front of the optical modulator 20. That is, the polarizing plate 60 may be disposed between the target scene (including, for example, the subject 200) and the optical modulator 20. The polarizer 60 may be a linear polarizer and/or a circular polarizer.

In an example, polarizer 60 may be a linear polarizer having an orientation with a polarization direction that is not parallel to the optical axis of optical modulator 20. By placing linear polarizer 60 between the target scene and optical modulator 20, the polarization of the optical signal propagating towards optical modulator 20 may be determined. The linear polarizer 60 may be a 0 ° polarizer, a 45 ° polarizer, a 90 ° polarizer, a 135 ° polarizer, or any other angle polarizer.

Although the provision of the linearly polarizing plate 60 in front of the optical modulator 20 results in a loss of a part of the light energy, by providing the linearly polarizing plate 60, the polarization state of the optical signal in the initial state can be made known, i.e., the initial polarization state W must be located at a certain point on the equator of the poincare sphere. In this way, the distance of points in the scene and/or the relative light intensity of points in the scene and other information can be determined by only one shot.

Accordingly, a method of ranging using a three-dimensional imaging system including the polarizer 60 may include: and shooting once at a preset time point to obtain image information, and determining the distance between each pixel point in the target scene and the optical emitter and/or the relative light intensity of each pixel point in the target scene based on the image information.

Fig. 7 shows a block diagram of a method of forming a three-dimensional imaging system 100 a.

Referring to fig. 7, in step S710, an optical modulator 20 is disposed on an optical path of the optical emitter 10 such that pulsed light emitted by the optical emitter 10 is received and modulated by the optical modulator 10 as it returns through the target scene. In step S730, an optical element array 30 is disposed on a path of outgoing light of the optical modulator 20 to receive the modulated light signal, wherein the optical element array 30 includes at least three polarizing plates having polarization directions different from each other. In step S750, the photodetector 40 is disposed behind the optical element array 30 to receive the optical signal passing through the optical element array 30 and convert the received optical signal into an electrical signal. In step S770, the controller 50 is provided to be electrically connected with the optical emitter 10, the optical modulator 20 and the photodetector 40, wherein the controller 50 is in communication with the optical emitter 10, the optical modulator 20 and the photodetector 40.

Controller 50 may apply a control voltage to the optical modulator 20, and the optical modulator 20 modulates the returned portion of the light pulse as a function of time based on the control voltage. The controller 50 may calculate the distance between each pixel in the target scene and the optical emitter 10 and/or the relative light intensity of each pixel in the target scene and other information based on the electrical signal from the photodetector 40 and the control voltage applied to the optical modulator 20.

In some embodiments, controller 50 applies control to optical modulator 20 through circuitry, and optical modulator 20 modulates the optical state of the returned portion of the light pulse as a monotonic function of time based on the control.

While the present disclosure includes specific examples, it will be apparent upon an understanding of the present disclosure that various changes in form and detail may be made in these examples without departing from the spirit and scope of the claims and their equivalents. The examples described herein are to be considered in a descriptive sense only and not for purposes of limitation. The description of features or aspects of the disclosure in each example will be considered applicable to similar features or aspects of the disclosure in other examples. Suitable results may also be achieved if the described techniques are performed in a different order and/or if components in the described systems, architectures, devices and/or circuits are combined in a different manner and/or replaced or supplemented by other components or their equivalents. Therefore, the scope of the present disclosure is defined not by the specific embodiments but by the claims and their equivalents, and all changes within the scope of the claims and their equivalents are to be construed as being included in the present disclosure.

Claims

1. A three-dimensional imaging system comprising:

an optical transmitter that transmits light pulses towards a target scene that returns at least a portion of the light pulses;

characterized in that the three-dimensional imaging system further comprises:

an optical modulator that modulates an optical state of at least a portion of the light pulses emitted from the optical emitter and/or returned from the target scene;

an array of optical elements receiving at least a portion of the modulated light pulses, wherein the array of optical elements has the function of transmitting light in at least three mutually different optical states, the optical states comprising at least one of polarization state, transmittance, reflectance, at least within a first preset time range before emission of the light pulses and/or within a second preset time range after emission of the light pulses;

a photodetector including an imaging lens that receives the optical signal passing through the optical element array and converts the received optical signal into an electrical signal; and

a controller applying control to the optical modulator through a circuit, the optical modulator modulating optical states of the light pulses emitted from the optical emitter and/or at least a portion of the light pulses returned from the target scene as a function of time based on the control, and the controller calculating distances between the pixels in the target scene and the optical emitter and/or relative light intensities of the pixels in the target scene based on the electrical signal from the photodetector and the control applied to the optical modulator.

2. The three-dimensional imaging system of claim 1, wherein the optical state is a polarization state of light.

3. The three-dimensional imaging system of claim 2, wherein the array of optical elements comprises at least three polarizers having fixed polarization directions that are different from each other.

4. The three-dimensional imaging system of claim 2, wherein the array of optical elements comprises at least one polarization component with adjustable polarization direction.

5. The three-dimensional imaging system of claim 2, wherein the array of optical elements is comprised of four polarizing components arranged in a checkerboard pattern.

6. The three-dimensional imaging system of claim 2, wherein the optical element array comprises at least one optical element array unit, each of the at least one optical element array unit comprising at least three polarization components having polarization directions different from each other; and

the photodetector includes at least one photodetector cell corresponding to the at least one optical element array cell.

7. The three-dimensional imaging system of claim 6, wherein the optical element array unit comprises four polarizers arranged in a checkerboard pattern.

8. The three-dimensional imaging system of claim 7, wherein the four polarizing components are a 0 ° directional linear polarizer, a 45 ° directional linear polarizer, a 90 ° directional linear polarizer, and a 135 ° directional linear polarizer, respectively.

9. The three-dimensional imaging system of claim 6, wherein three of the at least three polarizing components having polarization directions different from each other are a 0 ° directional linear polarizer, a 45 ° directional linear polarizer, and a left-or right-handed polarizer, respectively.

10. The three-dimensional imaging system of claim 3, wherein the array of optical elements comprises a thin film polarizer, a wire grid polarizer, a prismatic polarizer, a liquid crystal polarizer, or a combination thereof.

11. The three-dimensional imaging system of claim 1, wherein the optical modulator comprises a crystal, liquid crystal with electro-optic modulation effect, and/or a crystal, liquid crystal with acousto-optic modulation effect.

12. The three-dimensional imaging system of claim 1, wherein the optical modulator comprises a plurality of serially connected optical modulators.

13. The three-dimensional imaging system of claim 1, wherein the array of optical elements and the photodetector are integrally integrated.

14. The three-dimensional imaging system of claim 1, wherein the optical emitter and the photodetector are integrated integrally or separately.

15. The three-dimensional imaging system of claim 1, wherein the light pulse has a wavelength of 300nm-750nm, 700nm-1000nm, 900nm-1600nm, 1um-5um, or 3um-15 um.

16. The three-dimensional imaging system of claim 1, wherein the light pulse has a pulse width of 0.1ps-5ns, 1ns-100ns, 100ns-10us, or 10us-10 ms.

17. The three-dimensional imaging system of claim 1, wherein the photodetector comprises a silicon-based detector CCD, CMOS, and/or Ge, InGaAs, InSb, InAs, hgcace, QWIP detector, or detector array.

18. The three-dimensional imaging system of claim 1, further comprising a lens disposed proximate to a side of the target scene and/or a lens disposed between the optical modulator and the array of optical elements.

19. The three-dimensional imaging system of any of claims 1 to 18, further comprising a linear polarizer and/or a circular polarizer disposed on a side of the optical modulator proximate to the target scene.

20. A method of ranging using the three-dimensional imaging system of any of claims 1 to 19, comprising:

arranging an optical modulator on an optical path of an optical emitter so that pulsed light emitted by the optical emitter has a time-varying optical state as it returns through a target scene;

receiving the optical signal modulated by the optical modulator through an optical element array, wherein the optical element array comprises at least three polarization components having polarization directions different from each other;

disposing a photodetector behind the array of optical elements to receive optical signals passing through the array of optical elements and to convert the received optical signals into electrical signals; and

a controller is provided in electrical communication with the optical emitter, the optical modulator, and the photodetector, wherein the controller applies control to the optical modulator that modulates a return portion of the light pulse as a function of time based on the control, and the controller calculates a distance between each pixel in the target scene and the optical emitter and/or a relative light intensity of each pixel in the target scene based on the electrical signal from the photodetector and the control applied to the optical modulator.

21. The method of claim 20, wherein the controller applies control to the optical modulator via a circuit, the optical modulator modulating the optical state of the returned portion of the light pulse as a monotonic function of time based on the control.

22. A method of ranging using the three-dimensional imaging system of claim 1, comprising:

shooting the target scene for the first time at an initial time point to obtain reference image information; and

performing a second photographing at a next time point spaced apart from the initial time point by a predetermined time to obtain comparative image information,

wherein the distance between each pixel point in the target scene and the optical emitter and/or the relative light intensity of each pixel point in the target scene is determined based on the reference image information and the comparison image information.

23. A method of ranging using the three-dimensional imaging system of claim 19, comprising:

calibrating the three-dimensional imaging system;

and shooting once at a preset time point to obtain image information, and determining the distance between each pixel point in the target scene and the optical emitter and/or the relative light intensity of each pixel point in the target scene based on the image information and system calibration information.

24. A method of ranging using the three-dimensional imaging system of any of claims 1 to 19, comprising:

modulating, by the optical modulator, an optical signal returned by the pulsed light emitted by the optical emitter via the target scene;

receiving an optical signal passing through the optical element array using a photodetector, and converting the received optical signal into an electrical signal;

applying, by a controller, a control to the optical modulator, the optical modulator modulating a return portion of the light pulse as a function of time based on the control; and

calculating, by the controller, a distance between each pixel in the target scene and the optical emitter and/or a relative light intensity of each pixel in the target scene based on the electrical signal from the photodetector and the control applied to the optical modulator.

25. A method of ranging using the three-dimensional imaging system of any of claims 1 to 19, comprising:

receiving the optical signal modulated by the optical modulator through an optical element array, wherein the optical element array comprises at least one optical component which transmits light of at least three optical states different from each other at least for a predetermined time;